A Simple and Efficient Preparation of High-Purity and High-Yield Unsolvated Lithium Dodecaborate

We present a new and simple approach for the synthesis of lithium dodecaborate (Li2B12H12) in high purity and high yield, based on the reaction between borane dimethyl sulfide complex (DMS·BH3) and lithium borohydride (LiBH4) in glymes (monoglyme or diglyme). The reaction can conveniently be performed either in a Schlenk flask with or without reflux, or in an autoclave. This strategy exhibits various advantages over existing methods, including high product purity, high reaction yields (up to 96%), and operational simplicity. The enclosed system provided by an autoclave is shown to be more favorable for the synthesis of the B12H122– anion and enables obtaining the highest yields. The reaction mechanism has been investigated by 11B NMR spectroscopy, revealing a stepwise formation of B2H7−, B3H8−, B9H14−, B11H14− and B11H132− intermediates. This synthesis method is extended to the M2B12H12 (M = Li, Na, K) series, yielding metal dodecaboranes coordinated with glymes, characterized by single crystal X-ray diffraction. We show that glymes can be removed through simple exchange with weaker coordinating solvents like DMSO or H2O, followed by heating under vacuum.